1. Technical Field
The present invention relates to devices and methods for use in orthopedic spine surgery. In particular, the present invention relates to an adjustable spacing device configured to be placed between the spinous processes of at least two adjacent vertebrae and a method of using the device to treat spinal stenosis.
2. Background Art
The human spine is comprised of thirty-three vertebrae at birth and twenty-four as a mature adult. Between each pair of vertebrae is an intervertebral disc, which maintains the space between adjacent vertebrae and acts as a cushion under compressive, bending and rotational loads and motions. A healthy intervertebral disc has a great deal of water in the well hydrated nucleus pulposus, the center portion of the disc. The water content gives the nucleus a spongy quality and allows it to absorb spinal stress.
In a young healthy individual, the intervertebral disc also serves as a natural spacer between adjacent vertebrae thus allowing sufficient space in central spinal canal and intervertebral foramina to permit unimpeded nerve passage from the neural canal. In addition to injuries or disease of the intervertebral discs, the common condition of spinal stenosis can impinge upon neural and vascular structures leading to neurological compromise.
Spinal stenosis is a common condition resulting from the narrowing of the spinal canal, nerve root canals and intervertebral foramina causing nerve pinching which leads to persistent pain, lack of feeling and decreased physical activity. Spinal stenosis can be dynamic and postural in that the increased symptoms can be experienced during extension of the spine; such as during standing or walking, and during flexion of the spine, such as bending forward or sitting, can be lessen. Lumbar spinal stenosis is of two general types. The most common is degenerative stenosis, occurring in virtually the entire population as a result of the natural process of aging. It is a degenerative narrowing of the spinal canal, nerve root canals and intervertebral foramina caused by bone and/or ligament hypertrophy in local, segmental or generalized regions. The narrowing of nerve egress pathways from the vertebral column results in compression of spinal nerves and nerve roots, causing a constellation of symptoms, including lower back pain, neurogenic claudication and lower extremity pain. A second general type of spinal stenosis is congenital lumbar spinal stenosis, which is relatively rare and usually presents at an early age, often between 30 and 40. Acquired spinal stenosis is more common and general develops when patients are in their 60's or older. It is a condition that can neither be predicted nor prevented. It does not distinguish by sex, race, or ethnicity. Nor is it associated with any particular occupation or body type.
The most common indication for surgery in persons aged over 60 in the United States is lumbar spinal stenosis. Currently, it is estimated that as many as 400,000 Americans, most over the age of 60, may already be suffering from the symptoms of lumbar spinal stenosis and this number is expected to grow as members of the baby boom generation begin to reach their 60s over the next decade. According to the U.S. Census Bureau, people over 60 will account for 18.7% of the domestic population in 2010 versus 16.6% in 1999. According to the United Nations' Population Division, Department of Economic and Social Affairs, the trend is global with the number of persons aged 60 years or older estimated to be nearly 600 million in 1999 and is projected to grow to almost 2 billion by 2050, at which time the population of older persons will be larger than the population of children (0-14 years) for the first time in human history. The increasing prevalence of musculo-skeletal disorders and the cost to treat them led the World Health Organization and the United Nations to declare that 2000-2010 be the Decade committed to improving quality of life for people with bone and joint disease and injuries throughout the world.
It is this well recognized need to provide relief for a growing population of people suffering from spinal disease or injuries, particularly those suffering from spinal stenosis, that has prompted the increasing effort among orthopedic surgeons to find new methods and devices to provide that badly needed relief.